Various types of shower head dispensers have been used in the past to selectively dispense and mix liquid additives, such as soap, shampoo, or body oil, with the shower spray. For the most part, the typical shower head dispenser utilizes the aspirating effect of the shower spray to draw the liquid additive into the shower water. The typical shower head dispenser may include containers for several liquid additives and a manually operated valving arrangement is employed to selectively control the delivery of the liquid additives.
In the typical household, the water pressure is apt to fluctuate due to variations in the main pressure or by virtue of drawing water at other locations in the household. With shower head dispensers as used in the past, which operate on an aspirating action, variations in water pressure, or variations in water volume due to operation of the shower valve itself, result in a corresponding variation in the amount of liquid additive being dispensed. The shower head dispensers as used in the past have not been capable of maintaining a substantially uniform delivery of the liquid additive regardless of variations in water pressure.